Submillimeter-wave Josephson spectroscopy

A Josephson high-temperature superconducting (HTSC) submillimeter-wave spec trometer is designed, built, and experimentally investigated. The integrate d detection structure of the spectrometer includes a YBCO Josephson junctio n on a bicrystalline boundary, a double-slot or log-periodic antenna, and a low-inductance resistive shunt. The selective detector response and the re sponse at an intermediate frequency of 1.4 GHz are measured under the actio n of a signal in the frequency range 350-1250 GHz. Three methods of spectro scopy are investigated using this setup: 1) a method of Hilbert spectroscop y with processing of the detector response is implemented; 2) it is found t hat for a wide Josephson line at intermediate frequency (IF) the response h as the same form as the detector response, making it possible to obtain a s pectrum and the width of the generation line from IF response measurements; 3) for a narrow Josephson line the IF response corresponds to the regime o f conversion with self-pumping. A new method is proposed for calculating th e emission spectrum. The method consists of simple shift, summation, and su btraction operations. The advantages of the method are simplicity, high sen sitivity, and high resolution. (C) 1999 American Institute of Physics. [S00 21-3640(99)00517-4].